In ink jet printing of the continuous type, various techniques have been utilized to impress regularity on the break up of ink jet filaments issuing from the print head orifices. The use of vibrational energy of predetermined frequency is a common way to create uniformity in size and spacing of the droplets that form from the ink filaments. Such energy has been applied to the ink reservoir above the orifice plate or directly to the ink in such reservoir or to the orifice plate itself.
A relatively constant break-off point is highly desirable to effect reliable drop charging so that charged drops will be properly deflected to a catch or print trajectory. Where the printer system employs a plurality (an array) of orifices, it is particularly desirable that the break off of the various issuing filaments occur synchronously (i.e. that the drop streams are substantially in phase). This reduces the size of the "window" along the drop-path-length in which drop charging must occur and thus simplifies the printer structurally and electrically.
One highly useful system for imposing periodic vibrations to the drop streams is described in U.S. Pat. No. 4,646,104, which employs a pair of piezoelectric strips mounted on opposing longitudinal sides of a resonator block having: (i) a generally homogeneous composition and (ii) a resonant frequency approximately equal to the desired drop frequency. The strips are approximately perpendicular to the strips' orifice plate that is mounted on one end of the resonator block and are energized to expand and contact in unison along their length direction. In response, the resonator block vibrates to oscillate the orifice plate between substantially parallel planes that are normal to the longitudinal axis of the resonator. This "salt-shaker" type movement of the orifice plate creates reliable, in phase, break up of the ink filaments issuing from the orifices.
Although the above-mentioned system functions very well, it has the disadvantage of requiring a tuned resonant body construction. Also, particular systems are designed to operate respectively about a specific nominal drop frequency. Thus, the range of operable drop frequencies for a printer that employs a resonator of this type is limited.